The field of photovoltaics generally relates to multi-layer materials that convert solar radiation or sunlight energy into direct current (DC) electricity for the generation of electric power. These photovoltaic materials are commonly referred to as solar cells, and can be produced commercially in a thin-film configuration, such as by depositing one or more thin layers of photovoltaic material and supporting layers onto a substrate in a certain pattern and sequence. Thin film solar cells provide several advantages. One such advantage is that these compositions have a high cross-section for absorbing incident light. That is, photovoltaic layers that are very thin can capture a relatively high percentage of incident light. For example, in many thin film solar cell devices, photovoltaic layers may have a thickness in the range of from about 1 μm to about 4 μm. These thin layers allow devices incorporating these layers to be flexible. The characteristic flexibility of thin films further enables the solar cell material comprising numerous devices to be prepared in a continuous fashion, such as on a flexible web. This is in contrast to less flexible solar cells, such as those that comprise crystalline silicon, for example, which are typically fabricated and processed as discrete individual solar cells.
Because a single conventional solar cell typically cannot generate enough electricity for most applications, a number of solar cells can be electrically and physically connected to each other in an arrangement that is referred to as a photovoltaic module or “string”. Such modules or strings are designed to supply electricity at a certain voltage, where the electricity produced is directly proportional to the amount of sunlight that strikes the module. Multiple modules can in turn be attached to each other to form an array. In general, the larger the area of a module or array, the more electricity that will be produced. These modules and arrays can be connected in either series or parallel electrical arrangements to produce desired voltage and current combinations. In particular, electrical connections can be made in series to achieve a desired output voltage and/or in parallel to provide a desired amount of current source capability. In addition, a semiconductor junction develops a photo-voltage, while the area and other parameters of the device determine the available current. Commercially available solar panels are therefore designed to have an appropriate area and arrangement to deliver a certain amount of power and optimize other application parameters.
Photovoltaic arrays are often associated with buildings, where these arrays can be integrated into the building structure, mounted onto the building in some way (e.g., attached to the roof structure), or located separately from the building structure but connected by a cable or power supply to the building. In some cases, arrays are built as a part of the construction of a new building, and in other cases, the arrays are retrofitted into existing buildings. For one example, roof tiles have been developed that incorporate photovoltaic cells, where these tiles are used instead of traditional roofing shingles. In another application, solar cells can be incorporated into wall panels of a building, such as panels that can be incorporated into the siding structure or that may be attached to existing siding materials. Such roof tiles and/or wall panels can be incorporated into both domestic and industrial buildings as a primary or secondary source of electrical power for that structure.
As part of the process of fabricating thin film solar cell modules or strings, several processing steps must be carried out to connect multiple solar cells to each other, which can be referred to as an interconnection process. Such an interconnection process requires precise placement of interconnecting elements, which can be wires or flat wires (which are also referred to herein and known in the art as ribbons), for example, and solar cells in order to obtain mechanically robust solar cell strings that can be used in later processes that utilize those strings. This precise placement of wire ribbons relative to the solar cells also requires precise regulation of the dispensing of the conductive epoxy that functions as an adhesive. Precise control of mechanical tolerances is important to ensuring that the solar cell strings can easily be accommodated in downstream processes. Ensuring high accuracy and precision in processes for interconnecting thin film solar cells can be challenging operations compared to similar processes for rigid substrates, particularly due to the additional degrees of freedom that are afforded by the flexible nature of the thin film solar cell. Thus, there is a need to provide automated thin film solar cell interconnection equipment and methods for electrically connecting multiple solar cells in an efficient and accurate manner.